The present invention relates to an image pickup device and particularly to an image pickup device that uses a so-called phase-difference autofocus (AF) system.
Conventionally, a focus detection system, like the one disclosed in JP-A-1-266503, is well known. According to JP-A-1-266503, as shown in FIGS. 17A and 17B, the focus detection system is disposed on an optical path that passes through a picture-taking lens 501 and a quick return mirror, a half mirror, or the like (not shown). In the focus detection system, there are provided a planned imaging plane 502 of the picture-taking lens 501, and a field lens 503 disposed near the planned imaging plane 502. Moreover, a secondary optical system 504 (a re-imaging lens group) that includes secondary imaging lenses 541, 542, and 543. The secondary imaging lens 542 is so disposed as to be aligned with the optical axis of the imaging lens 501. The secondary imaging lenses 541 and 543 are so disposed as to be symmetrical about the optical axis of a picture-taking objective lens 1. A light receiving means 505 includes three light receiving element rows 551, 552, and 553. The three light receiving element rows 551, 552, and 553 are so disposed as to correspond to three secondary imaging lenses 541, 542, and 543. An aperture diaphragm 506 includes three openings 561, 562, and 563. The three openings 561, 562, and 563 are so disposed as to correspond to the secondary imaging lenses 541, 542, and 543. An exit pupil 507 of the picture-taking lens 501 is divided into three by the field lens 503 and the like.
In the focus detection system, a primary imaging plane (the planned imaging plane 502) is provided at a position that is substantially equivalent to an image pickup plane. A field diaphragm is disposed near the primary imaging plane to form a focus detection area. A condenser lens (the field lens 503) is disposed near the primary imaging plane. A brightness diaphragm (the aperture diaphragm 506) performs pupil division by using a plurality of openings. A plurality of re-imaging lenses (secondary imaging lenses) and light receiving element rows (the light receiving means 505) are each disposed according to the corresponding brightness diaphragm. Moreover, the condenser lens separately projects different areas of the picture-taking lens on the brightness diaphragm. Moreover, the re-imaging lenses projects an aerial image that exists at the position of primary imaging on the light receiving element rows through the corresponding brightness diaphragm.
In order to carry out detection for each of a plurality of focus detection areas, the focus detection system includes a pair of re-imaging lenses for each of the focus detection areas. The focus detection system uses one re-imaging lens for re-imaging of a plurality of focus detection areas.
As shown in FIGS. 17A and 17B, in the focus detection system, three focus detection areas line up in one direction on the surface of the field diaphragm. Moreover, in the focus detection system, a re-imaging lens group 504 including a pair of re-imaging lenses is so provided as to correspond to each of the focus detection areas. The re-imaging lens group 504 includes three re-imaging lenses 541, 542, and 543 that line up in one direction. The outer re-imaging lenses 541 and 543 both correspond to the central focus detection area and detect a focus. Moreover, one outer re-imaging lens 541 and the central re-imaging lens 542 correspond to the outer focus detection area and detect a focus. It is also disclosed that the focus detection system can be similarly disposed in a direction perpendicular to the plane of paper.
FIG. 18 illustrates a configuration aimed at making the focus detection system thinner and expanding a distance measurement area. According to the configuration illustrated in FIG. 18, a picture-taking optical system 201, a field diaphragm surface 202 that exists at a position equivalent to the image pickup plane, a field diaphragm 203 set near the field diaphragm surface 202, a condenser lens 204 disposed near the field diaphragm surface 202, a brightness diaphragm 205 disposed away from the condenser lens 204, a re-imaging lens group 206 disposed near the brightness diaphragm 205, and a light receiving member 207 corresponding to the re-imaging lens group 206 are disposed in that order from the object-of-shooting side.
The field diaphragm 203 includes an opening (also referred to as a field opening, hereinafter). Thanks to the field opening, a focus detection area is set. Moreover, the brightness diaphragm 205 is to perform pupil division and can be referred to as a pupil division diaphragm. The brightness diaphragm 205 includes a plurality of openings 205a1 to 205a3 and 205b1 to 205b3 (also referred to as pupil division diaphragm openings, hereinafter). Moreover, the re-imaging lens group 206 includes a plurality of re-imaging lenses 206a1 to 206a3 and 206b1 to 206b3. Moreover, the light receiving member 207 includes a plurality of photoelectric conversion sections 207a1 to 207a3 and 207b1 to 207b3. The photoelectric conversion sections each include a plurality of photoelectric conversion elements (light receiving elements). The photoelectric conversion elements (light receiving elements) are arranged in the same direction as the pupil division diaphragm openings are arranged.
Among the above components, the field diaphragm 203 (field openings), the condenser lens 204, the brightness diaphragm 205, the re-imaging lens group 206, and the light receiving member 207 are collectively referred to as a focus detection system in general.
In the focus detection system illustrated in FIG. 18, in order to realize the above object, the field diaphragm is formed by three field openings, and a member for detecting a focus is disposed for each of the field openings. In FIG. 18, virtual regions 208a and 208b are planned in the picture-taking lens 201. The field diaphragm 203 is disposed near the field diaphragm surface 202.
The field diaphragm 203 is formed by the field openings 2031, 2032, and 2033. The pupil division diaphragm openings 205a1 to 205b3, the re-imaging lenses 206a1 to 206b3, and the photoelectric conversion sections 207a1 to 207a3 are so disposed as to correspond to the individual field openings 2031, 2032, and 2033.
Moreover, the condenser lens 2041 is disposed near the field opening 2031. The pupil division diaphragm opening 205a1 is disposed at a conjugated position of the virtual region 208a by the condenser lens 2041. The re-imaging lens 206a1 is disposed near the pupil division diaphragm opening 205a1. The re-imaging lens 206a1 projects on the photoelectric conversion surface 207a1 an image formed on the field opening 2031 through the condenser lens 2041 and the pupil division diaphragm opening 205a1.
Similarly, the necessary structure for focus detection is realized by a combination of the virtual region 208b, the field opening 2031, the condenser lens 2041, the pupil division diaphragm opening 205b1, the re-imaging lens 206b1, and the photoelectric conversion surface 207b1, a combination of the virtual region 208a, the field opening 2032, the condenser lens 2042, the pupil division diaphragm opening 205a2, the re-imaging lens 206a2, and the photoelectric conversion surface 207a2, a combination of the virtual region 208b, the field opening 2032, the condenser lens 2042, the pupil division diaphragm opening 205b2, the re-imaging lens 206b2, and the photoelectric conversion surface 207b2, a combination of the virtual region 208a, the field opening 2033, the condenser lens 2043, the pupil division diaphragm opening 205a3, the re-imaging lens 206a3, and the photoelectric conversion surface 207a3, and a combination of the virtual region 208b, the field opening 2033, the condenser lens 2043, the pupil division diaphragm opening 205b3, the re-imaging lens 206b3, and the photoelectric conversion surface 207b3.